1. Technical Field of the Invention
The present invention relates to rotors for vehicular electric rotary machines and vehicular electric rotary machines using such rotors and, more particularly, to a rotor for a vehicular electric rotary machine such as an on-vehicle alternator, a vehicular electric rotary machine employing such a rotor, a method of manufacturing a rotor of a vehicular electric rotary machine and a method of manufacturing a vehicular electric rotary machine.
2. Description of the Related Art
In the related art, it has been a usual practice for vehicles to be installed with vehicle alternators as vehicular electric rotary machines. With such vehicle alternators, a rotor normally comprises Lundell-type claw-shaped poles carried on a rotary shaft and supported inside a stator carried on a housing. In order to allow magnetic fluxes to reliably exchange between the Lundell-type poles and the stator, permanent magnets have been provided each between sidewalls of the claw-shaped poles for preventing the magnetic fluxes from leaking between the claw-shaped poles. Further, another attempt has heretofore been made to prevent the permanent magnets from being thrown out of the rotor in a radially outward direction thereof to result in damages due to centrifugal forces acting on the permanent magnets.
As one of these technologies, a vehicle alternator has been proposed which includes a rotor having Lundell-type poles whose outer peripheries are provided with axially extending flange portions between which each permanent magnet is held in fixed place with magnet holding members being interconnected to each other with the use of a connecting member formed in a toric shape (see Patent Publication 1: Japanese Patent Unexamined Application Publication No. 10-313560 on pages 3 and 4 and in FIGS. 1 to 9).
U.S. Pat. No. 6,486,585 (Patent Publication 2) discloses a vehicle alternator including a rotor having Lundell-type poles. With such a vehicle alternator, after the rotor has been assembled, the rotor is subjected to a cutting step for forming flange portions on claw-shaped poles with grooves to allow permanent magnets to be inserted therein.
Meanwhile, it has been a common practice for the rotor to be cut on a final stage to take a rotational balance. When this takes place, the cutting causes the formation of iron chips and iron powder that tend to stick to the grooves of the rotor. These iron chips and iron powder are detached from the outer periphery of the rotor during rotation thereof with the resultant tendency of causing various issues such as defective rotation of the rotor. In addition, the iron chips and iron powder tend to jump out of the rotor into the wirings of the stator thereby causing damage to occur thereon with the resultant deterioration in insulation properties. Moreover, in the middle of a stage in which the permanent magnets are kept as stocks in a factory until their assemblies are completed as a rotor or in a way of delivery of non-assembled component parts, minute iron powder in the factory tends to stick to the rotor and enters the stator, thereby causing the same issues as those mentioned above. In order to address such issues, an attempt has heretofore been undertaken to provide technology with which non-magnetized magnets are preassembled to a rotor after which compensating cutting step is carried out to take a rotational balance of the rotor and, subsequently, the magnets are magnetized (see Patent Publication 3:
Japanese Patent Unexamined Application Publication No. 6-178474 on pages 3 to 6 and in FIGS. 1 to 13).
Although no disclosure is made in Patent Publication 1 on a time point at which the magnets are magnetized, the magnets may be possibly magnetized during the production of a rotor on a final stage thereof as disclosed in Patent Publication 3. With the rotor disclosed in Patent Publication 1, however, a need arises for the magnet holding members and the member for interconnecting these magnet holding members to be formed in a toric configuration. This results in increases in the number of component parts and man-hours, causing an issue to arise with an increase in production cost besides the cost of permanent magnet bodies.
With the vehicular electric rotary machine disclosed in Patent Publication 2, further, although the permanent magnets can be assembled to the rotor on a final stage, iron materials or iron powder, resulting from cutting to form the flange portions of the claw-shaped poles and the portions for the permanent magnets to be inserted, cause the field coil, wound inside the claw-shaped poles, to be damaged and remain in areas between the claw-shaped poles and the outermost circumferential periphery of the field coil. This causes another issue to arise with deficiencies occurring during the power generating operation of the vehicle alternator.
With the vehicular electric rotary machine disclosed in Patent Publication 3, furthermore, each of the permanent magnets extends not only to an area between the adjacent claw-shaped poles but also to another area facing the claw-shaped pole in an entire axial length thereof, thereby forming a toric configuration as a whole. With such a configuration, the permanent magnets of the rotor are made from synthetic resin mixed with magnetic powder. Such a structure results in a shortage of magnetic force for a leakage of magnetic fluxes to be prevented in a modern high power-output vehicle alternator. Another consequence is the rotor having a lack of strength for high-speed rotation of the rotor. Thus, it becomes hard to employ such an alternator as a vehicle alternator. In addition, since the permanent magnets surround the rotor in an entire circumference thereof throughout the axial length thereof, the amount of metallic raw material used for the magnet holding members also increases. Therefore, an issue arises with the vehicle alternator disclosed in Patent Publication 3 in that the production cost of the magnet holding members increases.